In general, when an industrial robot having a linked structure composed of a rotatable arm portion, a vertically movable shaft portion, and related devices is used to fix a worked article (workpiece) to an object article, it is possible that a related motion of a workpiece will deviate from a normal condition, for some reason, and an abnormal situation such as a collision of the workpiece with the object article occurs. Such an abnormality causes a failure of the robot and hinders the progress of the robot operation, and accordingly, effective measures are sought to minimize such problems and thus facilitate a smooth progress of the robot operation, although such appropriate measures have not yet been obtained.